diff --git a/libc/kernel/uapi/linux/loop.h b/libc/kernel/uapi/linux/loop.h
index ff3482f..d5a23b5 100644
--- a/libc/kernel/uapi/linux/loop.h
+++ b/libc/kernel/uapi/linux/loop.h
@@ -77,6 +77,7 @@
 #define LOOP_CHANGE_FD 0x4C06
 #define LOOP_SET_CAPACITY 0x4C07
 #define LOOP_SET_DIRECT_IO 0x4C08
+#define LOOP_SET_BLOCK_SIZE 0x4C09
 #define LOOP_CTL_ADD 0x4C80
 #define LOOP_CTL_REMOVE 0x4C81
 #define LOOP_CTL_GET_FREE 0x4C82